Strange substitution by HAL

This didn't cost me a game or anything, but can anyone speculate why HAL defensively subbed Dickie Thon for Omar Vizquel? Vizquel was not injured, he's a significantly better defender than Thon, he's a faster baserunner, and his hitting card is much better. Vizquel(6.80) Thon(.71). There are no strange settings in my team settings saying to remove Vizquel, it just seemed like a rather odd substitution. I can't see any strategical advantage to removing Vizquel for Thon. It's a DH league, so it wasn't double switch related. Thon had not appeared in a game all season to this point, was this just HAL giving him the equivalent of a participation trophy?

http://365.strat-o-matic.com/game/435466/135

Every once in a while, HAL does one of these wonky substitutions. One season, he would randomly put my backup catcher in for no good reason. Good news is it's rare this happens; bad news is you have no control over it happening.